An immunoassay is a test that relies on biochemistry to measure the presence and/or concentration of an analyte. The analyte can be large proteins, antibodies that a person has produced as a result of an infection or small molecules. These assays are highly adaptable and can be applied to many formats depending on the needs of the end user. The principle component of an immunoassay designed to detect a specific analyte, such as influenza nucleoprotein, are the antibodies that have been carefully selected to ensure the detection of the analyte at low concentration with high specificity, meaning will not react with similar antigens. The second feature of an immunoassay is the system that is designed to detect the binding of the specific antibody to the target analyte. Originally the signal from an immunoassay resulted from an enzyme acting on a substrate to yield a colored solution with the amount of color in the solution being equivalent to the amount of antigen in the test solution.